virtio-net: fix total qstat values

NIPA tests report that the interface statistics reported
via qstat are lower than those reported via ip link.
Looks like this is because some tests flip the queue
count up and down, and we end up with some of the traffic
accounted on disabled queues.

Add up counters from disabled queues.

Fixes: d888f04c ("virtio-net: support queue stat")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Link: https://patch.msgid.link/20250507003221.823267-3-kuba@kernel.org


Signed-off-by: Paolo Abeni <pabeni@redhat.com>